An Ultra Wide Band (UWB) signal occupies a wide frequency range due to its narrow pulse width. Various signal shapes can be used in order to meet frequency band restrictions and transmitter/receiver design requirements. The UWB signals are normally difficult to distinguish from noise. Various modulation schemes are used to detect and track a UWB signal and distinguish the signal from noise in a UWB receiver.
One such technique is to multiply the UWB pulse train by a synchronized, unique pseudo-random noise (PRN) code in the UWB transmitter. By correlating a received signal with the same code in a UWB receiver, the UWB signal train can be detected and recovered from noise. The signal output from a correlator includes a series of peaks in which some are “true” cross-correlation peaks representing a transmitted pulse, and others are “false” cross-correlation peaks representing signal noise. The “true” cross-correlation peaks are higher than the false peaks by some margin. The margin is determined by the length of the PRN code, the orthogonality properties of the code and how much noise and interference is present in the incoming signal. The operating range for UWB systems can be limited because the “safety margin,” that is, the margin between the true and false correlation peaks, quickly vanishes with distance due to propagation loss and multi-path loss.